/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:		arm_rms_q31.c
*
* Description:	Root Mean Square of the elements of a Q31 vector.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @addtogroup RMS
 * @{
 */


/**
 * @brief Root Mean Square of the elements of a Q31 vector.
 * @param[in]       *pSrc points to the input vector
 * @param[in]       blockSize length of the input vector
 * @param[out]      *pResult rms value returned here
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 *
 *\par
 * The function is implemented using an internal 64-bit accumulator.
 * The input is represented in 1.31 format, and intermediate multiplication
 * yields a 2.62 format.
 * The accumulator maintains full precision of the intermediate multiplication results,
 * but provides only a single guard bit.
 * There is no saturation on intermediate additions.
 * If the accumulator overflows, it wraps around and distorts the result.
 * In order to avoid overflows completely, the input signal must be scaled down by
 * log2(blockSize) bits, as a total of blockSize additions are performed internally.
 * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
 *
 */

void arm_rms_q31(
    q31_t* pSrc,
    uint32_t blockSize,
    q31_t* pResult)
{
	q63_t sum = 0;                                 /* accumulator */
	q31_t in;                                      /* Temporary variable to store the input */
	uint32_t blkCnt;                               /* loop counter */

#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	q31_t in1, in2, in3, in4;                      /* Temporary input variables */

	/*loop Unrolling */
	blkCnt = blockSize >> 2u;

	/* First part of the processing with loop unrolling.  Compute 8 outputs at a time.
	 ** a second loop below computes the remaining 1 to 7 samples. */
	while(blkCnt > 0u) {
		/* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
		/* Compute sum of the squares and then store the result in a temporary variable, sum */
		/* read two samples from source buffer */
		in1 = pSrc[0];
		in2 = pSrc[1];

		/* calculate power and accumulate to accumulator */
		sum += (q63_t) in1 * in1;
		sum += (q63_t) in2 * in2;

		/* read two samples from source buffer */
		in3 = pSrc[2];
		in4 = pSrc[3];

		/* calculate power and accumulate to accumulator */
		sum += (q63_t) in3 * in3;
		sum += (q63_t) in4 * in4;


		/* update source buffer to process next samples */
		pSrc += 4u;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* If the blockSize is not a multiple of 8, compute any remaining output samples here.
	 ** No loop unrolling is used. */
	blkCnt = blockSize % 0x4u;

#else

	/* Run the below code for Cortex-M0 */
	blkCnt = blockSize;

#endif /* #ifndef ARM_MATH_CM0 */

	while(blkCnt > 0u) {
		/* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
		/* Compute sum of the squares and then store the results in a temporary variable, sum */
		in = *pSrc++;
		sum += (q63_t) in * in;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */

	sum = __SSAT(sum >> 31, 31);


	/* Compute Rms and store the result in the destination vector */
	arm_sqrt_q31((q31_t)((q31_t) sum / (int32_t) blockSize), pResult);
}

/**
 * @} end of RMS group
 */
